This invention relates to rotary piston machines and, in particular, to rotary piston machines of the rotary-abutment type.
Rotary-abutment machines typically consist of a housing which contains two parallel cylindrical bores. A cylindrical piston is located in one bore and a cylindrical rotary abutment or sealing rotor is located in the other bore. The piston is provided with a plurality of lobes to provide surfaces for partitioning the housing bores into working volumes. The sealing rotor has a plurality of cavities cut in its circumference and is synchronized in rotation with the piston so that the lobes enter the cavities during operation. The piston and sealing rotor are physically arranged to maintain close clearance therebetween so that working fluid, trapped between the piston lobes, housing, and sealing rotor, is compressed or expanded according to the direction of rotation of the piston. To avoid friction which causes a reduction in efficiency and may require lubrication of parts in rubbing contact, many prior art designs have used noncontacting seals between the various components of the engine. A frictionless seal is usually constructed by aligning the moving parts with a small clearance between each of the moving members. One, or both, of the members is provided with a series of slots or grooves. Such a seal, which is usually known as a "labyrinth" seal, is effective because the working fluid, on passing through the sealing area, expands into each of the slots causing turbulence and the fluid must then regroup to pass through the next restriction. The result of the turbulence and regrouping is an effectively high resistance to leakage.
The efficiency of labyrinth seals is directly related to the distance the working fluid must traverse and the number of slots which are provided. Therefore, when labyrinth seals are utilized on a rotary-abutment machine, a serious seal problem develops at the seal between the piston and the sealing rotor. Since the piston and sealing rotor are in virtual contact tangentially and are both rotating, a very small area is involved over which the sealing can take place. Thus, labyrinth seals, which may be effective to seal the piston relative to the housing, are not effective to seal piston relative to the sealing rotor. Leakage at the seal between the piston and sealing rotor places an effective limit on the minimum speed at which the engine operates efficiently and reduces efficiency at low compression ratios.
Aother contributor to poor efficiency is excessive dead volume in the displacement mechanism. Excessive dead volume reduces the volumetric efficiency of the engine and typically arises when the valving operations (which are necessary to perform expansion or compression of the working fluid) are carried on outside of the housing cavities. Several prior art designs have attempted to utilize the sealing rotor as a valve on either the intake or the discharge port. These designs, however, have been unable to perform simultaneously three functions that are necessary in certain heat engine applications of rotary displacers:
1. One port must always be open. That is, the working volumes performing constant pressure processes must always be in communication with a heat exchanger volume connected to this port.
2. One port must be periodically closed off or "valved". That is, the working volumes in which compression or expansion of the working fluid takes place must be in communication with the connected heat exchanger volumes during the intake and exhaust processes and isolated from the heat exchanger volumes during the compression and expansion processes.
3. The working volumes in the main rotor and sealing rotor bores must always be in communication with each other during variable pressure (compression or expansion) processes.
In order that all three of the above requirements be satisfied, prior art designs have required that the valving function be performed by a separate valve mechanism rather than by the sealing rotor. Such designs entail a penalty in terms of the unswept volume (dead volume) in the passageway to or from this separate valving mechanism.
Therefore, there appears to be a need for a rotary piston machine with a small dead volume and improved volumetric efficiency and low internal leakage.
Accordingly, it is an object of the present invention to increase volumetric efficiency in a rotary piston machine.
It is another object of the present invention to reduce seal leakage between the piston and sealing rotor of a rotary-abutment machine.
It is a further object of the present invention to reduce the dead volume in a rotary piston machine.